The present invention generally relates to power supplies, and more particularly to a radiation tolerant, self-oscillating switching regulator with hysteretic voltage control to convert a DC input voltage to an intermediate DC output voltage.
Switching regulators typically provide near-constant voltage levels to voltage-sensitive devices. An example regulator includes a switch, an inductance-capacitance (LC) output filter to smooth the output, a feedback circuit, a comparator, and a control circuit. The control circuit selectively turns the switch on and off as necessary, based on a sample of a function of the output received by the comparator via the feedback circuit, to maintain the output voltage within a desired range.
Various types of switching regulators have been developed. One example includes a fixed frequency pulse width modulating (PWM) integrated circuit with a gate drive circuit and a derived voltage source for powering circuit components. The fixed frequency PWM circuit switches continuously, regardless of whether switching is necessary. Accordingly, the fixed frequency PWM circuit continuously generates undesirable electromagnetic interference and switching power losses. Conventional switching regulators typically require an additional regulator circuit to create a low voltage supply for the comparator to operate over a wide voltage range, resulting in an increased number of components and a corresponding increase in size, weight, and cost. Additionally, conventional switching regulators typically are not radiation hardened.
Many systems, particularly those in spacecraft, would benefit from a switching regulator that requires less space, operates reliably over a wide range of input voltages without the requirement of a separate regulator circuit to serve as a power supply, and has superior radiation tolerance.
The present invention provides a switching regulator connectable to a power supply. The switching regulator includes a first node connectable to the power supply, a feedback node, an output node, and a ground node. A power switch is coupled between the first node and the output node and has a power switch control gate. An output voltage feedback circuit is coupled between the output node and the feedback node, and to the ground node. A self-oscillating power switch control circuit is coupled to the first node, the ground node, the feedback node, and to the power switch control gate and compares a feedback voltage at the feedback node to a reference voltage. The self-oscillating power switch control circuit provides a first control voltage to the power switch control gate when the reference voltage exceeds the feedback node voltage to turn on the power switch to thereby raise the output node voltage to a desired level. The self-oscillating power switch control circuit provides a second control voltage to the power switch control gate when the feedback node voltage exceeds the reference voltage to turn off the power switch to thereby lower the output node voltage to a desired level.
In one embodiment of the switching regulator, an output filter is coupled between the power switch and the output node to smooth the output voltage waveform.
In one embodiment of the switching regulator, the self-oscillating power switch control circuit includes a voltage reference circuit to provide a desired reference voltage. In one aspect, the voltage reference circuit includes a first temperature-compensated voltage reference diode having an anode and a cathode. A constant current diode is coupled between the first node and the cathode of the first temperature-compensated voltage reference diode. A second temperature-compensated voltage reference diode has a cathode coupled to the anode of the first temperature-compensated and an anode coupled to a first terminal of a resistor whose second terminal is coupled to the ground node. Additionally, a capacitor is coupled between the cathode of the first temperature-compensated voltage reference diode and the anode of the second temperature-compensated voltage reference diode to reduce in-rush current by slowing the turning-on of the power switch.
In one embodiment of the switching regulator, the self-oscillating power switch control circuit includes a comparator circuit and a power switch biasing circuit. The comparator circuit compares the reference voltage to the feedback voltage and the power switch biasing circuit provides the first control voltage and the second control voltage to turn the power switch on and off.
In one embodiment, the comparator circuit comprises a first n-channel transistor with a gate coupled to a reference voltage node, a drain coupled to the power switch biasing circuit, and a source. A second n-channel transistor has a gate coupled to an output voltage reference node, a drain coupled to the power switch biasing circuit, and a source. A resistor has a first terminal connected to the sources of both n-channel transistors and a second terminal connected to the ground node.
In one embodiment, the power switch biasing circuit comprises a first p-channel transistor with a gate coupled to both the drain of the first n-channel in the comparator circuit and to a first terminal of a first resistor whose second terminal is coupled to the input node, a source coupled to the power switch control gate, and a drain coupled to the anode of the second temperature-compensated voltage reference diode in the voltage reference circuit. A second p-channel transistor has a source coupled to the input node, a drain connected to the power switch control gate, and a control gate. A second resistor has a first terminal coupled to the input node and a second terminal coupled to the gate of the second p-channel transistor. A third resistor has a first terminal coupled to the gate of the second p-channel transistor, and a second terminal coupled to the drain of the second n-channel transistor in the comparator circuit. A fourth transistor has a first terminal coupled to the input node, and a second terminal coupled to the power switch control gate.
One aspect of the present invention provides a method for providing a desired second DC voltage level from a power supply having a first DC voltage level. The method includes receiving the first DC voltage level from the power supply and comparing the first DC voltage level from the power supply to the desired second DC voltage level. A first control voltage level is provided to a power switch control gate to cause the power switch to turn on if the first DC voltage level is less than or equal to the desired second DC voltage level to thereby provide the first DC voltage level at an output node. A first control voltage level and a second control voltage level are alternately provided to the power switch control gate to cause the power switch to turn on and off if the first DC voltage level is greater than the desired second DC voltage, thereby turning the power switch on and off at an appropriate switching frequency to thereby provide the desired second DC voltage level.
In one embodiment, the present invention provides a switching regulator control circuit that utilizes only four active devices, such as metal-oxide semiconductor field-effect transistors (MOSFETs). In one embodiment, the switching regulator includes a comparator, a driver for a MOSFET power switch, and a control circuit which provides hysteresis voltage control.